Do you know anything about a rainbow-like cloud-is it unusual?

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by Jeff Renner

Bio | Email | Follow: @Jeffrennerwx

KING5.com

Posted on July 3, 2014 at 10:45 PM

Do you know anything about a rainbow-like cloud-is it unusual?

Yes...but no, it's not that unusual. It's actually not a rainbow-the colored arc forms when sunlight passes through ice crystals in high clouds, bending and separating into the component colors of light. A particular type of ice crystal is required-flat, six sided 'plates'. If sunlight strikes, enter and then passes through the crystals at the right angle...then we see what's called a 'circumhorizon arc'. Such arcs require the sun to be high in the sky-conditions make such arcs most likely to be seen in the Pacific Northwest from May to August.

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